As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized sheet packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material. The packaging material has a multilayer structure comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or of mineral-filled polypropylene material, and which is covered on both sides with layers of thermoplastic material, e.g. polyethylene film. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material comprises a layer of oxygen-barrier material, e.g. aluminium foil, which is superimposed on a layer of thermoplastic material, and is in turn covered with another layer of thermoplastic material eventually forming the inner face of the package contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent such as a hydrogen peroxide solution, which is subsequently removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
The above packages are normally fitted with reclosable opening devices to protect the food product inside the package from contact with external agents, and to enable the product to be poured out.
At present, the most commonly marketed opening devices comprise a frame defining a pour opening for the food product, and fitted about a removable or pierceable portion of a top wall of the package; and a cap hinged or screwed to the frame, and which is removable to open the package. Alternatively, other types of opening, e.g. slide-open, devices are also known to be used.
The removable portion of the package may be defined, for example, by a so-called “prelaminated” hole, i.e. a hole formed in the base layer of the packaging material before covering the base layer with the layers of thermoplastic material and the layer of barrier material, which close the hole to ensure hermetic, aseptic sealing, while at the same time being easily pierceable.
Alternatively, the hole may be formed through the full thickness of the packaging material and covered with an additional so-called “patch” defined by a small sheet of thermoplastic material having a layer of oxygen-barrier material.
In one particularly advantageous solution described in the Applicant's Patent Application EP-A-1081054, the frame comprises an annular-flanged fastening portion fixed about the removable portion of the packaging material; and the cap has a cylindrical anchoring portion extending through the pour opening in the frame and fixed, preferably heat-sealed, directly to the removable portion covering the hole in the packaging material, so that, when removing the cap from the frame, the removable portion remains attached to the cap and is detached from the rest of the top wall of the package. In other words, to unseal the package, the user simply acts on the cap to detach the cap from the frame and detach the removable portion in one operation.
The above solution has since been improved further (as described in the Applicant's European Patent Application n. EP-A-1352840) by modifying the frame to form a further fastening portion having a tubular cylindrical liner extending about the anchoring portion of the cap, covering the edge of the hole in the packaging material, and fixed at one axial end to a peripheral edge of the removable portion.
The above alteration provides first and foremost for improving unsealing of the package and pour-out of the food product. That is, by virtue of the fastening portion with the cylindrical liner being fixed to the periphery of the removable portion, the anchoring portion of the cap is fixed to a better laminated, more radially inner portion of the removable portion, thus ensuring clean removal of the packaging material about the pour opening. Moreover, the fastening portion of the frame with the cylindrical liner defines a rigid contrast member, against which the material of the removable portion is torn, thus making the package easier to unseal, even when using particularly hard-to-tear thermoplastic materials, such as metallocene and LK25.
Once the removable portion is detached, the fastening portion with the cylindrical liner also prevents the hole from absorbing the food product, which, as is known, may occur when the package is left in a horizontal position for a relatively long period of time (eight hours on average), and which, particularly in the case of aggressive food products such as fruit juice, may result in detachment of the opening device.
Though advantageous and effective, the solutions described still leave room for further improvement, particularly as regards the precision with which the anchoring portion is fixed to the removable portion, and, hence, the precision with which the removable portion is detached from the package.
That is, given the inevitable tolerances between the cap and frame, the anchoring portion of the cap may not be centred perfectly with respect to the removable portion, thus resulting in less than perfect detachment of the removable portion when unsealing the package.